Evidence That a Decrease in Liver Glycogen Content Stimulates FFA Mobilization During Exercise

Abstract

This study evaluated a liver glycogen content decrease before exercise on the metabolic responses during exercise. Rats injected with glucagon (20 μg•kg−1) were compared to rats with a 50% food restriction (1/2-fast) and normally fed rats. All were studied at rest and during exercise (26 m/min, 0% grade). Resting liver glycogen concentrations were twice as high (P < .01) in normally fed rats, with no significant differences between 1/2-fast and glucagon-injected rats. During exercise, liver glycogen content was significantly reduced in normally fed rats. After exercise, plasma insulin levels were decreased (P < .01) in all groups, and β-hydroxybutyrate concentrations were similar in normally fed and glucagon-injected rats and significantly (P < .01) lower in 1/2-fast rats. Exercise caused a significant increase in FFA concentrations in all groups (P < .01). No significant differences in FFA concentrations were found between 1/2-fast and glucagon-injected groups (P > 0.05). Key words: glucagon injection, fasting, insulin, hepatic receptors